1. Field of the Invention
This invention relates generally to the field of wet chemical processing and more specifically to methods for controlling the composition of baths used in chemical processing, especially those baths used in plating processes. Specifically, the invention relates to semiconductor processing methods and apparatus for accurately controlling the concentration of chemical constituents which vary over time due to any of several causes.
2. Description of the Prior Art
In the field of chemical processing it is important that the composition and concentration of various constituents be controllable. The use of chemical wet processing has been used in semiconductor manufacturing since its inception in the early 1950s. Control of chemical composition has not been considered a problem in applications such as rinsing and cleaning as the implemented chemical processes were not based on a critical material balance. In such instances, excess volume of reagents or other constituents was a common practice, as little reliance was placed on, or was needed on, the accurate control of reactions or reaction rates.
More recently, there has been an increasing interest in providing accurate control over the composition of any number of chemical processing parameters. Perhaps the most critical area of increased interest has been in that of chemical plating, particularly that of electroplating.
The following patents relate to the controlling of chemical constituents in various applications including electroplating bath composition stabilization. Each patent is hereby incorporated in its entirety for its respective teaching and disclosure.
U.S. Pat. No. 5,192,403 entitled xe2x80x9cCYCLIC VOLTAMMETRIC METHOD FOR THE MEASUREMENT OF CONCENTRATIONS OF SUBCOMPONENTS OF PLATING SOLUTION ADDITIVE MIXTURESxe2x80x9d and U.S. Pat. No. 5,196,096 entitled xe2x80x9cMETHOD FOR ANALYZING THE ADDITION AGENTS IN SOLUTIONS FOR ELECTROPLATING OF PbSn ALLOYSxe2x80x9d issued to Chang et al., relate to concentration measurement techniques which are useful in evaluating the effects of additions of various components in electroplating bath solutions.
U.S. Pat. No. 5,312,532 entitled xe2x80x9cMULTI-COMPARTMENT ELECTROPLATING SYSTEMxe2x80x9d issued to Andricacos et al. describes an electroplating system in which semiconductor wafers may be plated with copper.
U.S. Pat. No. 5,352,350, entitled xe2x80x9cMETHOD FOR CONTROLLING CHEMICAL SPECIES CONCENTRATION,xe2x80x9d to Andricacos et al., describes a method of controlling the concentration of chemical species in a wet chemical bath by calculating the change in concentration of species based on known changes based on process-active species, non-process-active, deliberate, non-deliberate and time-active changes. Each species was modeled based on several factors, including, but not limited to, material balance, addition of feed stock, as well as time dependent changes such as evaporation or other deleterious events. This patent is relied herein on for the more general aspects of predictive dosing.
U.S. Pat. No. 5,385,661, entitled xe2x80x9cACID ELECTROLYTE SOLUTION AND PROCESS FOR THE ELECTRODEPOSTION OF COPPER-RICH ALLOYS EXPLOITING THE PHENOMENON OF UNDERPOTENTIAL DEPOSITION,xe2x80x9d to Andricacos et al., describes a plating bath comprising a number of additives which require control during plating.
U.S. Pat. No. 5,631,845, entitled xe2x80x9cMETHOD AND SYSTEM FOR CONTROLLING PHOSPHATE BATH CONSTITUENTS,xe2x80x9d TO Filev et al., relates to methods of controlling composition of a chemical system by using feedback from a measured quantity of a constituent to control the flow rate of the constituent.
To practice electroplated copper-interconnect technology, the copper must be electroplated under precisely controlled conditions. The key to manufacturing control, high yield, and manageable cost of a chemical reaction-based process is control of the composition of the reaction bath, especially the concentrations of certain organic and/or inorganic additives present in the bath. Existing methods and apparatus for bath-composition control are marginally acceptable at best. This is especially true for the use of electroplating in semiconductor processing. Particularly problematic is the tendency for bath additives to fluctuate in concentration because their rates of consumption depend on factors and conditions that are not controlled or accounted for in the present art. There is a strong need to reduce such fluctuations and thereby to achieve highly stable process performance in manufacturing.
It is therefore an object of the invention to provide precise control of the constituents in a practical and automatic manner which requires little overhead.
It is another object of the invention to provide a chemical bath controlling system in which different modes of operation are utilized to determine the changes to be anticipated in the system.
It is a further object to provide a method for controlling the chemical characteristics of a bath which requires little human intervention by using predictive dosing.
These objects are accomplished by parsing the daily operating time periods of a chemical system into distinct operating modes in which depletion or increases in bath components may vary in a manner differently that in other modes.
Examples of distinct operating modes include standby, system active (without the process working on a workpiece) and active or working reaction mode.
These and other objects of the invention will become more apparent in view of the following more particular description of the invention and drawing.